Greywater can be treated and reused in the field as irrigation water. The water can be diverted without altering the existing plumbing system. If you want to reuse water from the washing machine, you can pump out the water that you need out of the machine and use the water on the plants. Washing machines have an inbuilt pump that makes pumping of the water quite easy.
If you do not have a budget for buying the greywater treatment system, are living in a rented apartment or the area between your house and the lawn to be irrigated is made of a concrete patio, you may install a laundry drum. Water is pumped into a large sludge drum that offers temporary storage of the greywater. The water then drains at the bottom through a hose to the field that it is to be irrigated. The method is cheap but requires the hose to be moved to irrigate the whole of the desired area.
A laundry-to-landscape system gives the flexibility in the plants that you would like to irrigate and requires very little maintenance. You do not need to alter the plumbing to use the system. You can connect the washing machine to the diverter valve for the flow of water to the plants. The system directs water towards tubing that is directed to specific plants. The system is easy to install and very flexible for irrigation. It also ensures that the intended plants do get the water.
Water from the shower and sinks
The showers provide relatively clean greywater, which can be used for irrigation. A simple system should make use of the gravity to take the water to the field. You can have a branched drain that splits the flow into smaller sizes of tubes so that the right amount of water reaches they intended plants. The system is time-consuming but easy to manage when it is completed.
The water from the kitchen sink has a lot of organic matter content. In some states, the water is regarded as blackwater. To prevent the water from clogging the system, it is good to use mulch basins where the matter collects before the water is used for irrigation. The bathroom sink can be combined with the shower drainage for irrigation purposes.
To learn more of the water treatment and conservation, you can enroll at Open Permaculture School and check Regenerative Leadership Institute at their online portal. The school teaches various disciplines in water management, collection, and conservation.